Review for Dictionary Switcher by borekb
Rated 3 out of 5 stars
This is such an essential add-on for anyone typing in more than one language in Firefox, unfortunately, it hasn't been updated in a while and doesn't work well with e.g. Gmail, it can freeze the whole Firefox for short amounts of time, etc. But it's a really good idea.
To create your own collections, you must have a Mozilla Add-ons account.